Screening for both genetic diseases and chromosomal defects with a single biopsy improves pregnancy rates

Couples who are undergoing pre-implantation genetic diagnosis (PGD) in order to avoid transmission of inherited diseases, such as Duchenne muscular dystrophy or cystic fibrosis, should also have their embryos screened for abnormal numbers of chromosomes at the same time, say Italian researchers.
By doing this, only embryos that are free not only of the genetic disease, but also of chromosomal abnormalities (aneuploidy), would be transferred to a woman’s womb, giving her the best chance of achieving a successful pregnancy, and avoiding the risk of implantation failure, miscarriage, or even live births that could be affected by conditions such as Down syndrome (in which there is an extra chromosome) or Turner syndrome (in which a girl has only one x chromosome rather than the normal two).
In a study reporting on the world’s largest series of double genetic tests the researchers carried out simultaneous PGD and pre-implantation genetic screening (PGS) on cells taken in a single biopsy.
They took between five and ten cells from the outer layer of 1122 blastocysts (the early collection of cells that begin to form about five days after an egg has been inseminated with sperm and which go on to develop into an embryo) and, after PGD and PGS, 218 blastocysts were transferred to the women’s wombs, resulting in 99 pregnancies and the birth of 70 healthy babies by January 2017, when the paper was written. This is a pregnancy rate of 49%, which is higher than the average clinical pregnancy rate of between 22-32% reported in the general population of couples undergoing in vitro fertilisation (IVF). At the time of writing the paper, 13 further pregnancies were ongoing and now 12 have resulted in the birth of healthy babies, while one miscarried. This gives a delivery rate of 38.6%. A total of 91 healthy blastocysts remain frozen awaiting transfer.
Dr Maria Giulia Minasi, laboratory director at the Centre for Reproductive Medicine, European Hospital, Rome, Italy, and first author of the study, said: “Importantly, we found that while 55.7% of the biopsied blastocysts did not carry a genetic disease or changes in the structures of chromosomes, only 27.5% of them also had the right number of chromosomes. Without performing pre-implantation genetic screening for aneuploidy, 316 blastocysts, which appeared to be healthy but had abnormal numbers of chromosomes, could have been transferred, leading to implantation failures, miscarriages or sometimes live births of babies affected by aneuploidy. For the couples involved, and particularly the women, these outcomes can be emotionally devastating.”
As a result of their findings, Dr Minasi and her colleagues believe that when couples undergo PGD, they should also have PGS.

The European Society of Human Reproduction and Embryology
www.eshre.eu/Press-Room/Press-releases-2017/Simultaneous-PGD-and-PGS-screening-on-cells-in-a-single-biopsy.aspx